Supplemental pulldown mechanism for carburetor automatic choke

ABSTRACT

The carburetor has a conventional automatic choke construction heating a bimetallic coil by engine exhaust stove heat to slowly open the choke valve during cold weather starts; a supplemental temperature responsive power means operable above a predetermined ambient temperature in response to engine acceleration demand moves the choke valve open faster, to reduce emissions.

United States Patent [191 Freismuth et al.

[45] Aug. 27, 1974 SUPPLEMENTAL PULLDOWN MECHANISM FOR CARBURETORAUTOMATIC CHOKE Inventors: Richard J. F reismuth, Mt. Clemens;

Thomas R. Johnson, Ann Arbor,

both of Mich.

Assignee: Ford Motor Company, Dearbom,

Mich.

Filed: Aug. 16, 1973 Appl. No.: 389,066

References Cited UNITED STATES PATENTS 6/1967 Winkler et al. 261/39 BPrimary Examiner-Wendell E. Burns Attorney, Agent, or Firm-Keith L.Zerschling; Robert E. McCollum [57] ABSTRACT The carburetor has aconventional automatic choke construction heating a bimetallic coil byengine exhaust stove heat to slowly open the choke valve during coldweather starts; a supplemental temperature responsive power meansoperable above a predetermined ambient temperature in response to engineacceleration demand moves the cholke valve open faster, to reduceemissions.

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SUPPLEMENTAL PULLDOWN MECHANISM FOR CARBURETOR AUTOMATIC CHOKE Thisinvention relates, in general, to a carburetor for a motor vehicleengine. More particularly, it relates to an automatic choke to providecold weather starts of an engine, and yet good accelerations withoutstalls, while at the same time minimizing the output of undesirableemissions.

As ambient temperature drops, friction within the engine and theviscosity of the lubricants increase significantly. Therefore, at lowtemperatures, the speeds at which an engine normally would idle must beincreased to prevent stalling. Accordingly, a choke mechanism isgenerally provided to lessen the air intake during cold starting andpre-engine warmup to insure a richer mixture.

Generally, the choke apparatus includes a coiled thermostatic springthat operatively rotates the choke valve towards a closed or nearly shutposition with decreasing temperatures, and progressively opens it as thetemperature returnstowards a chosen level. A manifold suction responsivedevice generally cracks open the choke a predetermined amount when theengine starts. The choke action provides a rich mixture so thatsufficient fuel can be vaporized to permit smooth cold weather startingand running of the engine.

The above construction, while generally satisfactory, is a compromisebetween good cold weather running conditions on the one hand and lowemission outputs on the other hand. The richer than normal mixtureexisting during the choking operation may be richer than is necessary,which may result in higher emission outputs.

It is an object of this invention to provide an automatic chokeconstruction that will provide good cold weather startingcharacteristics, provide good accelerations without stall, and yetreduce to a minimum the output of undesirable smog producing elements.

It is another object of the invention to provide an automatic chokeconstruction that provides a leaner than conventional air/fuel mixtureafter the start of a warm engine in response to engine accelerationdemand by pulling open the choke valve faster than would be byconventional choke systems.

It is also an object of the invention to provide an automatic chokeconstruction including a temperature responsive, delayed action servooperable above a predetermined ambient temperature as controlled by theengine throttle valve to shorten the length of time required for thenormal operation of an automatic choke.

Another object of the invention is to'provide an automatic chokeconstruction including a thermostatically controlled bimetal springnormally urging the choke valve closed with decreasing ambienttemperature changes and opposed by 'a manifold suction operated motordevice that initially cracks open the choke valve to a predeterminedamount permitting running operation during cold weather with a richmixture; engine exhaust manifold heat being directed to the spring coilto warm it; and, a supplemental vacuum operated servo operable atambient temperatures above a predetermined level during engineacceleration modes to positively open the choke valve earlier than wouldnormally be the case, the supplemental servo including a temperatureactuated valve permitting the application of man ifold vacuum uponopening of the throttle valve to pull the choke valve open, the vacuumacting through a parallel path including a one-way check valve toprevent choke valve reapplication during low vacuum, and a restrictionthat allows recycling of the servo.

Other objects, features and advantages of the invention will become moreapparent upon reference to the succeeding detailed description thereof,and to the drawings illustrating a preferred embodiment thereof; whereinFIG. 1 is a cross-sectional elevational view of a portion of atwo-barrel carburetor embodying the inventIOIl;

FIG. 2 is a perspective view of a carburetor with the automatic choke ofthe invention;

FIG. 3 is a side elevational view of a portionof the FIG. 2 showing,with parts broken away and in section;

FIG. 4 is an enlarged cross-sectional view of a detail of FIG. 3; and,

FIG. 5 is a cross-sectional view taken on a plane indicated by andviewed in the direction of the arrows 5-5 of FIG. 4.

FIG. l'is obtained by passing a plane through approximately one-half ofa known type of two-barrel, downdraft type carburetor. The portion ofthe carburetor shown includes an upper air horn section 12, anintermediate main body portion 14, and a throttle valve flange section16. The three carburetor sections are secured together by suitablemeans, not shown, over an intake manifold indicated partially at 18leading to the engine combustion chambers.

Main body portion 14 contains the usual air-fuel mixture inductionpassages 20 having fresh air intakes at the air horn ends, and connectedto manifold 18 at the opposite ends. The passages are each formed with amain venturi section 22 containing a booster venturi 24 suitably mountedfor cooperation therewith, by means not shown.

Airflow through passages 20 is controlled in part by a choke valve 28unbalance mounted on a shaft 30 rotatably mounted on side portions ofthe carburetor air horn, as shown. Flow of fuel and air through eachpassage 20 is controlled by a conventional throttle valve 36 fixed to ashaft 38 rotatably mounted in flange portion 16. The throttle valves arerotated in a known manner by depression of the vehicle acceleratorpedal, and move, from an idle speed position essentially blocking flowthrough passage 20 to a wide open position essentially at right anglesto the position shown.

The rotative position of choke valve 28 is controlled by asemi-automatically operating choke mechanism 40. The latter includes ahollow housing portion 42 that is formed as an extension of thecarburetor throttle flange. The housing is apertured for supportingrotatably one end of a choke lever operating shaft44, the opposite endbeing rotatably supported in a casting 46. A bracket or lever portion 48is fixed on the left end portion of shaft 44 for mounting the end of arod 52 that is pivoted to choke valve shaft 30. It will be clear thatrotation of shaft 44 in either direction will corre spondingly rotatechoke valve 28 to open or close the carburetor air intake, as the casemay be.

An essentially L-shaped thermostatic spring lever 54 has one leg 56fixedly secured to the opposite or righthand end portion of shaft 44.The other leg portion 58 of the lever is secured to the end 59 of acoiled thermostatic spring element 60 through an arcuate slot, notshown, in an insulating gasket 61. The opposite end portion 62 of thespring is fixedly secured on the end of a nipple 64 that is formed as anintegral portion of a choke cap 66 of heat insulating material. Nipple64 is bored as shown to provide hot air passages 68 and 70, passage 68being connected to an exhaust manifold heat stove, for example. Cap 66is secured to housing 42 by suitable means, such as the screw 72 shown,and defines an air or fluid chamber 74 within the two.

As thus far described, it will be clear that the thermostatic springelement 60 will contract or expand as a function of the changes inambient temperature conditions of the air entering tube 68, or, if thereis no flow, the temperature of the air within chamber 74. Accordingly,changes in ambient temperature will rotate the spring lever 54 to rotateshaft44 and choke valve 28 in one or the other directions, as the casemay be.

The, leg 56 of spring lever 54 is pivotally fixed to the rod 76 of apiston 78. The latter is movably mounted in a bore 79 in housing 42. Theunder surface of piston 78 is acted upon by vacuum in a passage 80 thatis connected to the carburetor main induction passages 20 by a port 82that is located just slightly below throttle valve 36. Piston 78,therefore, is always subject to the vacuum existing in the intakemanifold passage portion 18.

As is known, a cold weather start of a motor vehicle requires a richermixture than a warmed engine start because considerably less fuel isvaporized. Therefore, the choke valve is shut or nearly shut to increasethe pressure drop thereacross and draw in more fuel and less air. Oncethe engine does start, however, then the choke valve should be openedslightly to lean the mixture to prevent engine flooding as a result ofan excess of fuel.

The known choke mechanism described automatically accomplishes theaction described. That is, on cold weather starts, the temperature ofthe air in chamber 74 will be low so that spring element 60 willcontract and rotate shaft 44 and choke valve 28 to a closed or nearlyclosed position, as desired. Upon cranking the engine, vacuum in passage80 will not be sufficient to move piston 78 to open the choke valve.Accordingly, the engine will be started with a rich mixture. As soon asthe engine is running. high vacuum in passage 80 moves piston 78downwardly and rotates shaft 44 a slight amount so that choke valve 28is slightly opened so that less fuel is admitted to induction passage20. Shortly thereafter, the exhaust manifold stove air in line 68 willbecome progressively warmer and cause choke element 60 to unwind slowlyand rotate shaft 44 and choke valve 28 to a more open position. Furtherdetails of construction and operation are not given since they are knownand believed to be unnecessary for an understanding of the invention.

FIG. 2 shows the carburetor as including a supplemental choke valvepulldown servo device 90 that is connected to the choke rod lever 48.More specifically, and referring'to FIGS. 2-5, the servo 90 has a threepiece housing consisting of a left-hand vacuum line adapter portion 92,a main body portion 94, and a cup shaped shell portion 96.

Portion 92 has a press fit within an annular flange 98 projecting frombody portion 94, and contains a vacuum passage 100, with an orifice 101.

Body portion 94 contains an annular flange 122 and a central vacuumpassage 124. A Belleville type bimetal disc 126 is floatingly mountedwithin flange 122, and is biased towards the left by a spring 128. Thecentral portion of disc 126 has an elastomeric valve 130 fixed to itthat is adapted to seat against the passage 124 to control flow throughit. In assembly, an enlarged flexible integral portion 132 of the valveis pulled through a small hole 131 in disc 126 until the valve isseated, as shown.

The bimetal disc 126 is responsive to ambient temperature changes. ofthe servo to flip over-center from the full line position shown, to thedotted line position 133, in a known manner, at say, temperature levelsabove 65: for example, to open passage 124. Reduction of the ambienttemperature below the predetermined level will again flip-flop the discto close passage 124.

The disc spring 128 is seated against a cup shaped spring retainer 134.The latter is held in place in the ring flange 122 by a ring 136, andhas a central aperture 138.

The housing portions 94 and 96 together define a hollow interior.Between them is clamped the edge of an annular flexible diaphragm thatdivides the interior into an air chamber 142 and a vacuum chamber 144.I-Ioles 145 in housing portion 96 permit a free communication of chamber142 with the ambient air pressure surrounding the servo.

A pair of retainers 146 fixedly mount a plunger or link 148 on thediaphragm, a spring 150 normally biasing the plunger to the positionshown. The plunger has a lost motion connection to choke lever 48consisting of an elongated slot 152 that receives the bent end 154 of alink 156 pivotally connected to lever 48.

A pair of bosses 158 are welded to housing portion 96 for the attachmentof a mounting bracket 160 that is secured at its opposite end to aportion of the throttle valve body portion of the carburetor, as shown.

In this case, as best seen in FIG. 3, a tube 102 connects servo vacuumline 100 to a vacuum port 162 through a flow control device 164. Theport 162 opens into the carburetor induction passage 20 at a locationabove the cold fast idle position of the throttle valve 36. This is sovacuum will not be applied to line 102 until the engine is accelerated,in a manner to be described later, and will be cut off when the throttlevalve is returned to its idle speed position.

The control device 164 is shown schematically, and constitutes a checkvalve assembly. It has a hollow casing 166 with a central partition 168having two holes 170 and 172. A flexible elastomeric umbrella type checkvalve 174 controls flow through hole 170, while a sintered metalrestrictor 176 controls flow through hole 172. As will become more clearlater, once servo 90 has opened the choke valve, low vacuums at port 162will close check valve 174 to prevent a reclosing of the choke, whilethe restrictor 176 permits a bleeddown of vacuum in servo 90 and arestroking of the servo after engine shutdown.

In operation, below 65F ambient, the bimetal disc 126 remains in a valveclosed position as shown, and no vacuum is applied from passage 100 intoservo chamber 144 regardless of the position of throttle valve 36.Therefore, the servo is inoperative. The choke valve is initially closedby coil 60, and cracked open upon engine startup by the pulldown servo78. Increases in choke housing temperature, caused by the increases inexhaust manifold heat, cause the bimetal 60 to unwind slowly and permitopening of the choke valve by airflow against it. This is permitted bythe sliding movement of the pin 154 in slot 152. The entire chokingaction will then be controlled solely by the coil 60.

Assume now that the ambient temperature is above 65F. Vacuum now can beapplied directly to chamber 144 because the thermostatically responsivedisc 126 has now flipped over center to position 133. Check valve 174will open because of the pressure differential acting on opposite sides.Accordingly, when the throttle valve 36 is moved to an open engineacceleration position beyond the cold fast idle position shown, thevacuum port 162 becomes exposedto manifold vac uum. Thus, with servodisc 126 in position 133, vacuum in line 102 unseats valve 130 and openspassage 124. Manifold vacuum in passage 100 now is applied to begindrawing diaphragm 140 and plunger 148 to the left. This will continuewithout any effect on the choke valve until the pin 154 is engaged bythe end of slot 152. Continued leftward movement of the plunger until itbottoms, at dotted line position 162, against retainer 134, will thenpositively open the choke valve against the force of the coil 60.

The maximum delay in the system that occurs is determined by the size oforifice 101 and approximately 2 to 3 seconds, long enough so that thechoke valve will come off after the engine acceleration. This provides aricher mixture during the initial tip in accelerating movement of thethrottle valve.

Assume now that the engine is shut off so that the manifold vacuumdecays suddenly. It is desirable at this time that the servo 90 recycleitself so as to be in a position to provide the desired choking actionwhen restarted. The sintered metal bleed provides this action bybleeding the vacuum in chamber 144 to atmospheric pressure in line 102.

In summary, therefore, below an ambient temperature level of 65: F, thechoke hot air system provides the only control for choking functions.The bimetal coil 60 will unwind, therefore, only as a function of theincreased heating by the hot air from passage 68.

Above 65F, however, the conventional exhaust manifold stove heat systemconstitutes the primary choke control, while the vacuum operated servodevice 90 acts as the supplemental force to pull open the choke valvefaster than were it being controlled by the primary control alone. Thisleans the fule/air mixture earlier than with conventional chokearrangements, and lowers undesirable emission outputs. Control of thepulloff of the choke by the throttle valve prevents stalling duringacceleration modes of operation, and the check valve prevents the chokefrom being reapplied during low vacuum operating conditions.

With the above described choke construction, therefore, it will be seenthat it is possible to provide a reliable and accurate short. durationchoking effect thereby minimizing vehicle exhaust emission withoutjeopardizing the cold weather choking function.

We claim:

1. An automatic choke system for use with a carburetor having anair/fuel induction passage and an unbalance mounted, air movable, chokevalve mounted for variable movement across the passage to controlairflow through the passage,

a throttle valve mounted for a rotatable movement across the inductionpassage to open and close the same,

thermostatic spring means operably connected to the choke valve urgingthe choke valve towards a closed position with a force increasing as afunction of decreases in the temperature of the spring means from apredetermined level,

and a vacuum actuated, spring returned servo operable on the choke valvein opposition to the thermostatic spring means to at times override thechoke valve closing force of the thermostatic spring means and actuatethe choke valve to an open ineffective position, conduit meansconnecting a portion of the servo to a port in the induction passage ata location above the cold idle speed, slightly open, position of thethrottle valve so as to be subjected to ambient pressure duringoperation of the throttle valve in the cold idle speed position andsubjected increasingly to engine intake manifold vacuum as the throttlevalve is moved progressively across the port towards a position moreopen than the cold idle speed position indicative of an engineaccelerating condition.

2. A choke system as in claim 1 including temperature responsive meansin the conduit means for closing the conduit means below a predeterminedtemperature level.

3. A choke mechanism as in claim 1, including time delay means in theconduit means to control the application of pressure and vacuum to theservo.

4. A choke system as in claim 1, including time delay means in theconduit means to delay the bleed of vacuum from the servo upon openingof the throttle valve providing vacuum levels at the induction passagelower than at the servo, and one-way check valve means in parallel withthe delay means in the conduit means for bypassing the delay meansduring reverse vacuum conditions.

5. A two phase automatic choke system for use with a carburetor havingan air/fuel induction passage open at one end and adapted to beconnected to an engine intake manifold at the other end for subjectingthe passage to varying manifold vacuum, the passage having a throttlevalve mounted for a variable movement between positions opening andclosing the passage to control air/fuel flow through it,

the choke system including an unbalance mounted, air movable, chokevalve mounted anterior of the throttle valve for variable movementacross the passage to control air flow towards the throttle valve,

bimetallic thermostatic spring means operably connected to the chokevalve urging the choke valve towards a closed position with a forceincreasing as a function of decreases in the temperature of the springmeans from a predetermined level,

first power means sensitive to engine manifold vacuum for moving thechoke valve towards a partially open position in opposition to thespring means,

and supplemental vacuum sensitive power means in a parallel power flowarrangement with the first power means for effecting subsequent movementof the choke valve towards a position more open than the positioneffected by the first power means,

the supplemental means including a vacuum servo having a vacuum chamberand an ambient pressure chamber defined by a movable diaphragm, aplunger secured to the diaphragm, lost motion means connecting theplunger to the choke valve, conduit means connecting a port in theinduction passage to the servo vacuum chamber, the port being locatedabove the cold idle speed position of the throttle valve and adapted tobe traversed by the valve during its movement to an open engineaccelerating position beyond the cold idle speed position, the change inpressure in the vacuum chamber upon change in pressure in the conduitcluding on-off temperature responsive valve means in the conduit meansmovable to block flow of vacuum to the servo chamber below apredetermined ambient temperature.

7. An automatic choke system as in claim 5, the last mentioned controlmeans comprising a flexible check valve,

1. An automatic choke system for use with a carburetor having an air/fuel induction passage and an unbalance mounted, air movable, choke valve mounted for variable movement across the passage to control airflow through the passage, a throttle valve mounted for a rotatable movement across the induction passage to open and close the same, thermostatic spring means operably connected to the choke valve urging the choke valve towards a closed position with a force increasing as a function of decreases in the temperature of the spring means from a predetermined level, and a vacuum actuated, spring returned servo operable on the choke valve in opposition to the thermostatic spring means to at times override the choke valve closing force of the thermostatic spring means and actuate the choke valve to an open ineffective position, conduit means connecting a portion of the servo to a port in the induction passage at a location above the cold idle speed, slightly open, position of the throttle valve so as to be subjected to ambient pressure during operation of the throttle valve in the cold idle speed position and subjected increasingly to engine intake manifold vacuum as the throttle valve is moved progressively across the port towards a position more open than the cold idle speed position indicative of an engine accelerating condition.
 2. A choke system as in claim 1 including temperature responsive means in the conduit means for closing the conduit means below a predetermined temperature level.
 3. A choke mechanism as in claim 1, including time delay means in the conduit means to control the application of pressure and vacuum to the servo.
 4. A choke system as in claim 1, including time delay means in the conduit means to delay the bleed of vacuum from the servo upon opening of the throttle valve providing vacuum levels at the induction passage lower than at the servo, and one-way check valve means in parallel with the delay means in the conduit means for bypassing the delay means during reverse vacuum conditions.
 5. A two phase automatic choke system for use with a carburetor having an air/fuel induction passage open at one end and adapted to be connected to an engine intake manifold at the other end for subjecting the passage to varying manifold vacuum, the passage having a throttle valve mounted for a variable movement between positions opeNing and closing the passage to control air/fuel flow through it, the choke system including an unbalance mounted, air movable, choke valve mounted anterior of the throttle valve for variable movement across the passage to control air flow towards the throttle valve, bimetallic thermostatic spring means operably connected to the choke valve urging the choke valve towards a closed position with a force increasing as a function of decreases in the temperature of the spring means from a predetermined level, first power means sensitive to engine manifold vacuum for moving the choke valve towards a partially open position in opposition to the spring means, and supplemental vacuum sensitive power means in a parallel power flow arrangement with the first power means for effecting subsequent movement of the choke valve towards a position more open than the position effected by the first power means, the supplemental means including a vacuum servo having a vacuum chamber and an ambient pressure chamber defined by a movable diaphragm, a plunger secured to the diaphragm, lost motion means connecting the plunger to the choke valve, conduit means connecting a port in the induction passage to the servo vacuum chamber, the port being located above the cold idle speed position of the throttle valve and adapted to be traversed by the valve during its movement to an open engine accelerating position beyond the cold idle speed position, the change in pressure in the vacuum chamber upon change in pressure in the conduit means, to maintain the movement of the supplemental means during low vacuum conditions at the vacuum port.
 6. An automatic choke construction as in claim 5, including on-off temperature responsive valve means in the conduit means movable to block flow of vacuum to the servo chamber below a predetermined ambient temperature.
 7. An automatic choke system as in claim 5, the last mentioned control means comprising a flexible check valve. 